Chapter 4—Environmental Analysis, Consequences, and Mitigation 4.8 Geologic Hazards The information provided in this section was taken from the Westside Subway Extension Geotechnical and Hazardous Materials Technical Report. Additional information and details are provided in that report. 4.8.1 Regulatory Setting This section provides the state, and local regulations that are applicable to the geologic concerns of the Project and its Study Area. The Project would run through the incorporated cities of Los Angeles, Beverly Hills, West Hollywood and Santa Monica, and unincorporated portions of Los Angeles County. In addition to the National Environmental Policy Act of 1969, a Federal regulation, the following are applicable State and local regulations. State California Environmental Quality Act of 1970 The California Environmental Quality Act (CEQA) establishes a means to maintain and restore environmental quality for the public welfare. Under CEQA, the focus of the environmental analysis is on the physical change resulting from a project. However, the analysis of such changes may be traced back to non-physical changes, such as a revision in the use of an area that would cause physical changes. Alquist-Priolo Earthquake Fault Zoning Act The Alquist-Priolo Earthquake Fault Zoning Act (Public Resource Code [PRC]. 2621 et seq.) is the principal California state guidance to prevent the construction of habitable structures on the surface trace of active earthquake faults. The Alquist-Priolo Earthquake Fault Zoning Act only addresses the hazard of surface fault rupture and does not consider other earthquake hazards. Seismic Hazards Mapping Act The Seismic Hazards Mapping Act of 1990 (PRC 2690-2699.6) addresses non-surface fault rupture earthquake hazards, including liquefaction and seismically induced landslides. Surface Mining and Reclamation Act The Surface Mining and Reclamation Act (PRC 2710 et seq.) was established by the State Mining and Geology Board to regulate areas that are known to contain mineral deposits judged to be important in meeting the future needs of the region. California Health and Safety Code Section 25316 and 25317 of the California Health and Safety Code identify hazardous material, substances and wastes that require removal, including petroleum and petroleum by-products. Draft Environmental Impact Statement/Environmental Impact Report 4-143 Local Municipal Regulatory Approach The incorporated cities of Los Angeles, Beverly Hills, West Hollywood and Santa Monica, and Los Angeles County have engineering departments that administer and oversee geotechnical, subsurface, and seismic concerns. Each of these entities have general plan geologic elements and zoning codes to address geotechnical, subsurface and seismic concerns. Existing Conditions/Affected Environment Study Area Topography All the Project alternatives are located on the coastal plain of the Los Angeles Basin in an area that ranges between one-third and three miles south of the Santa Monica Mountains. Study Area elevations range between 400 and 85 feet above mean sea level (AMSL) from east to west. Study Area topography is mildly undulated to relatively flat from east to west. Table 4-40 shows the amount of topographic change in the Study Area. As shown in the table, the greatest difference in elevation of any one alignment segment is 215 feet over an approximate 4-mile segment. Table 4-40. Topography of Alternatives along Wilshire Boulevard Segment Approximate Approximate Change in Distance Elevation From To (in miles) (in feet) Alternatives Running Along Wilshire Boulevard Western Avenue La Brea Avenue 2 -5 La Brea Avenue Santa Monica Blvd and Wilshire 3.75 +73 intersection Santa Monica Blvd and Wilshire Westwood 2.25 +40 Boulevard intersection Westwood 405 Freeway 0.5 +10 405 Freeway W. Project Terminus at 4th Street 4 -215 Alternatives Originating at Hollywood/Highland Station Hollywood/ Highland Station Santa Monica Boulevard / San 3.25 -170 Vicente Boulevard Intersection Santa Monica Boulevard / San Vicente San Vicente Boulevard / Wilshire 1.5 -70 Boulevard Intersection Boulevard Intersection Sources: Section 3.1 Draft Geotechnical and Hazardous Material Technical Report with distances checked in GIS. Study Area Geology Geological Setting The Project area lies at the northern end of the northwesterly trending Peninsular Ranges physiographic province, to the south of the east-west trending Transverse Ranges physiographic province. The Peninsular Ranges physiographic province includes the nearby San Jacinto and Santa Ana mountains. The Transverse Ranges physiographic province includes the Santa Monica Mountains. 4-144 Westside Subway Extension September 2010 Chapter 4—Environmental Analysis, Consequences, and Mitigation The Los Angeles Basin which lies between the two physiographic provinces is an elongated northwest trending, sediment filled trough that is nearly 6 miles deep. At its surface the Los Angeles Basin is an alluvial coastal plain, comprised mainly of river deposited sediments originating from the nearby mountains. In the Project area the sediments originated primarily from the south flank of the Santa Monica Mountains. Geology A geological unit is a volume of rock of an identifiable origin and age that is defined by its distinctive and dominant features. Five to six geologic units exist within the tunnel and station depth horizon within the Project area. These are shown below in Table 4-41. Surficial geology in the Project area is shown on Figure 4-46. Surficial geology in relation to the Project tunnel is shown on Figure 4-47. Table 4-41. Geologic Units1 Geologic Age Formation (1000’s of Alternatives Age (age) years) Symbol Composition Location in Project Area Underlain Youngest Younger Recent to Qal1 Poorly consolidated, interlayered Western half of Beverly Hills, 1-5 Alluvium 1-12 Qal2 silts, clays, and silty sands with West Hollywood -Hollywood/ (Holocene) some sand layers and gravel Highland down to Wilshire Boulevard; La Jolla to Carmelina; and younger- alluvium-filled ravines from Western to La Jolla. Older 12-80 Qao Non-marine and marine All areas 1-5 Alluvium sediments. (Late Pleistocene) Lakewood 12-80 Qalo Upper portion: Interbedded silts Hancock Park/La Brea Tar 1, 2 and 3 (Pleistocene) and clays, sands, silty sands with Pits area to an area between some clayey sand layers. Lower South Crescent Heights and portion: interlayered silts and South La Jolla Boulevards sandy clays with some silty sand. San Pedro 2-500 Qsp Fine-grained sand and silty sand Wilshire Boulevard. from 1,2, and 3 (Pleistocene) with few interbeds of medium- to Western to La Jolla course-grained sand and some local silt layers. Some asphaltic sand found. Fernando 1,500- Tf Predominantly massive siltstone Hancock Park Area, Windsor 1 (Pliocene) 2,500 and claystone with few rare to Fairfax Avenue sandstone interbed Oldest Puente 5,500- Tp Massive siltstone and intervals of Near bottom of tunnel from 1 (Miocene) 10,000 claystone that are Interbedded Windsor to Fairfax with thin sandstone and siltstone laminae Sources: Section 3.2.2 Draft Geotechnical and Hazardous Material Technical Report. 1Units appearing at any depths ranging from the ground surface to bottom of the tunnel Draft Environmental Impact Statement/Environmental Impact Report 4-145 Figure 4-46. Surface Geology and Earthquake Faults 4-146 Westside Subway Extension September 2010 Chapter 4—Environmental Analysis, Consequences, and Mitigation Figure 4-47. Geological Cross Section Draft Environmental Impact Statement/Environmental Impact Report 4-147 Study Area Faulting, Seismicity, Seismic Hazards and Other Hazards The project Study Area lies within a seismically active region. The most significant seismic sources to the Project are listed in Table 4-42. Fault traces are delineated by the United States and California Geological Surveys (USGS and CGS). The locations of the faults shown in Table 4-42, and those in the Study Area are also shown in Figure 4-46. Table 4-42. Active Faults and Fault Segments Fault or Approximate Distance to Approximate Maximum Credible Fault Segment Study Area (in miles)1 Earthquake Magnitude (Mw)2 Santa Monica 0 6.6 Hollywood 0.25 6.4 Newport-Inglewood 1.75 7.1 Malibu Coast 2 6.7 Upper Elysian Park 2 6.4 Puente Hills 2..5 6.6—single segment rupture 7.1—multi-segment rupture Raymond 4.5 6.5 Palos Verdes 5.5 7.3 Compton 6 6.8 Verdugo-Eagle Rock 10 6.9 Sierra Madre 11 7.2 Anacapa-Dume 11.75 7.5 Northridge 13.75 7.0 San Fernando 14.25 6.7 Whittier 14.75 6.8 Santa Susana 17 6.7 San Andreas (Mojave) 33 7.4 Source: Table 3.1: Summary of Potential Seismic Sources in Section 3.2.4 Draft Geotechnical and Hazardous Material Technical Report. Distances shown originally in kilometers were converted to miles and approximated. 1Distances represent the distance from the closest trace of the fault to the closest portion of any of the Project alternative alignments. 2The moment magnitude scale (denoted as Mw) is now used by seismologists rather than the former Richter scale. Magnitude is based on the moment of the earthquake, which is equal to the rigidity of the Earth multiplied by the average amount of slip on the fault and the size of the area that slipped. The scale retains the familiar Magnitude scale of 1 to 10 defined by Richter.Faults Crossing the Project Area Known faults crossing the Project area include multiple segments of the Santa Monica Fault. The Santa Monica Fault is an east-west trending fault that is part of the Southern Boundary Fault System of the aforementioned Transverse Ranges Physiographic Province. It has not produced any moderate or large earthquakes in the historic record. However, it has been suggested that the fault has had at least six rupture events in the last 50,000 years, with the most recent being between 1,000 and 3,000 years ago. Based on evident changes in the area’s geologic structure, it appears that active segments of the Santa Monica Fault would cross portions of Alternatives 1 (MOS 2), 2, 3, 4 and 5.